Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor. The rotor typically includes a rotatable hub having one or more rotor blades attached thereto. The rotor blades capture kinetic energy of wind using known airfoil principles. For example, rotor blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is geared to a generator for producing electricity.
The lift force is generated when the flow from a leading edge to a trailing edge creates a pressure difference between the top and bottom surfaces of the blade. Ideally, the flow is attached to the top surface from the leading edge to the trailing edge. However, when the angle of attack of the flow exceeds a certain critical angle, the flow does not reach the trailing edge, but leaves the surface at a flow separation line, which decreases potential energy production.
Flow separation depends on a number of factors, such as incoming air flow characteristics (e.g. Reynolds number, wind speed, in-flow atmospheric turbulence) and characteristics of the blade (e.g. airfoil sections, blade chord and thickness, twist distribution, pitch angle, etc). The detached-flow region also leads to an increase in drag force, mainly due to a pressure difference between the upstream attached-flow region and the downstream detached-flow region. Flow separation tends to be more prevalent near the blade root due to the relatively great angle of attack of the blade flow surfaces in this region as compared to the blade tip.
Hence, in order to increase the energy conversion efficiency during normal operation of the wind turbine, it is desired to increase the lift force of the blades while decreasing the drag force. To this purpose, it is advantageous to increase the attached-flow region and to reduce the detached-flow region by moving flow separation nearer the trailing edge of the blade. It is known in the art to change the aerodynamic characteristics of wind turbine blades by adding dimples, protrusions, or other structures on the surface of the blade. These structures are often referred to as “vortex generators” and serve to create local regions of turbulent airflow over the surface of the blade as a means to prolong flow separation and thus optimize aerodynamic airflow around the blade contour. Such vortex generators, dimples, protrusions, and other similar features on the surface of the blade may be generally referred to herein as “airflow modifying elements.”
Conventional vortex generators typically consist of a base having one or more raised surfaces and are attached to the suction side of the blade using adhesive tape. It is important to properly align these airflow modifying elements in order to obtain the desired air flow characteristics, therefore, installation accounts for much of the time and cost associated with these features. For example, various systems may utilize cumbersome templates arranged on the surface of the rotor blade, which may take hours to install. Such systems may limit production to approximately two blades per day.
Accordingly, the industry would benefit from an improved method and assembly for aligning airflow modifying elements on the surface of a rotor blade. More specifically, a method and assembly that decreases installation time and cost would be advantageous.